Liquid crystal display devices are currently used in a variety of applications. In a general display device, one picture element consists of three pixels respectively representing red, green and blue, which are the three primary colors of light, thereby conducting a display operation in colors.
A conventional liquid crystal display device, however, can reproduce colors that fall within only a narrow range (which is usually called a “color reproduction range”), which is a problem. FIG. 81 shows the color reproduction range of a conventional liquid crystal display device that conducts a display operation using the three primary colors. Specifically, FIG. 81 shows an xy chromaticity diagram according to the XYZ color system, in which the triangle, formed by the three points corresponding to the three primary colors of red, green and blue, represents the color reproduction range. Also plotted by crosses x in FIG. 81 are the colors of various objects existing in Nature, which were disclosed by Pointer (see Non-Patent Document No. 1). As can be seen from FIG. 81, there are some object colors that do not fall within the color reproduction range, and therefore, a liquid crystal display device that conducts a display operation using the three primary colors cannot reproduce some object colors.
Thus, to broaden the color reproduction range of liquid crystal display devices, a technique that increases the number of primary colors used for display purposes to four or more has recently been proposed. For example, Patent Document No. 1 discloses a liquid crystal display device in which one picture element P consists of six pixels R, G, B, Ye, C and M representing the colors red, green, blue, yellow, cyan and magenta, respectively, as shown in FIG. 82. The color reproduction range of such a liquid crystal display device is shown in FIG. 83. As shown in FIG. 83, the color reproduction range, represented by a hexagon of which the six vertices correspond to those six primary colors, covers almost all object colors. By increasing the number of primary colors for use in display in this manner, the color reproduction range can be broadened.
Patent Document No. 1 also discloses a liquid crystal display device in which one picture element consists of four pixels representing the colors red, green, blue and yellow and a liquid crystal display device in which one picture element consists of five pixels representing the colors red, green, blue, yellow and cyan. In any case, by using four or more primary colors, the color reproduction range can be broadened compared to conventional liquid crystal display devices that use only the three primary colors for display purposes. Such liquid crystal display devices that conduct a display operation using four or more primary colors will be collectively referred to herein as “multi-primary-color liquid crystal display devices”.
In order to further improve the display quality of such multi-primary-color liquid crystal display devices, other techniques have recently been proposed. For example, Patent Document No. 2 discloses a technique for representing a brighter color red by providing two pixels representing the color red (i.e., first and second red pixels R1 and R2) for each picture element P in a multi-primary-color liquid crystal display device as shown in FIG. 84.                Patent Document No. 1: PCT International Application Japanese National Stage Publication No. 2004-529396        Patent Document No. 2: Pamphlet of PCT International Application Publication No. 2007-034770        Non-Patent Document No. 1: M. R. Pointer, “The Gamut of Real Surface Colors,” Color Research and Application, Vol. 5, No. 3, pp. 145-155 (1980)        